A certificate of authenticity (COA) is an inexpensive physical object that is more expensive to replicate than the product or circumstance that it certifies as authentic. A COA has a random unique structure that provides both a unique ID and an avenue for authenticating the unique ID. Additional desirable characteristics of a COA are that the uniqueness of the COA's random structure can be verified using an inexpensive device and/or at some distance from the COA.
From an economic standpoint, a COA is a digitally signed physical object that has a random unique structure for which the cost of creating and signing original COAs is small, relative to a desired level of security. The cost of manufacturing a COA instance should be several orders of magnitude lower than the cost of exact or near-exact replication of the unique and random physical structure of the instance. The cost of verifying the authenticity of a signed COA is also small, again relative to a desired level of security.
An additional characteristic, mainly impacted by desired level of usability, is that a COA must be robust to ordinary wear and tear. To this end, COA instances can be created in numerous ways. For example, when covering a substrate with an epoxy layer, the epoxy particles form a low-rise but randomized 3-dimensional (3-D) landscape that uniquely reflects light directed from a certain position. Such COAs were used for weapons control during The Cold War. There are also COAs created as a collection of optical fibers randomly positioned in an object using a transparent gluing material which permanently fixes the fibers' positions. Readout of the random structure of such a fiber-based COA can be performed in a number of ways using the fact that if one end of a fiber is illuminated, the other end will also glow. Fiber-based COAs have been proposed for banknote protection—the fibers being fixed by a semi-transparent material such as paper.
Only a few efforts have followed these initial forays into creating certificates of authenticity. For example, creating a class of physical one-way functions via speckle scattering has been tried by focusing on Gabor wavelets to produce short digests of the natural randomness collected from an optical phenomenon.
A fiber-based COA scanner prototype has been created, as well as a system for automatically verifying fiber-based COAs to emphasize the impact of point-subset compression on COAs' forging costs. Finally, COAs in the electromagnetic domain have been proposed by several companies such as TAPEMARK (St. Paul, Minn.) and CROSSID (Israel), all of them aiming to detect an RFID's random structure in the far-field. Such detection is prone to spoofing; in addition, such RFIDs can be relatively easily replicated. Also, because detection takes place in the far-field, both of these systems operate in the expensive 60 GHz frequency sub-band.